Refractory carbide composition



Patented Feb. 13,

UNITED 'Srras FFLICQE REFRACTORY OE COMPOSITION Franz B... Hansel, Indianapolis, Ind assignor to P. R. Mallory & 00., Inc., Indianapolis, hit, a corporation of Delaware No Drawing. Application Feb giary 24, I989,-

, Serial No.

2 Claims.

This invention relates to the production of a metallic composition particularly suitable for electric contact purposes.

This application is a continuation in part of -5-' prior filed application Serial No. 165,171, flied Another object of the invention is to provide I electrical contacting members which do not weld together as a result of arcing, at the time the contacts are engaged or disengaged.

- A further object of the invention is to improve the methods of producing the above noted char- 2 acteristics. A still further object of this invention is to 'provide circuit interrupter contacts that withstand the arcs incident to the operation-pf the contacts.

5 Other objects of the invention will beapparent from the following description taken in connection with the appended claims.

The present invention comprises the combination of elements, methods-of manufacture, and

the product thereof brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferred embodiment of the invention is described herein, it is contemplated thatconsiderable variation maybe made in the method of procedure and the combination of elements without departing from the spirit of the in:- vention.

A frequent cause of failure in electric contacts of the prior art has resulted from increase in contact resistance during operation until the contact resistance becomes too high and causes heating of the contacts to destructive temperatures. Critical current densities in the parts ac-t tually in contact often locally heat the contacts until fusion occurs, which subsequently welds the contacts to one another. Contacts also become welded together by the arc incident to the operation of the contacts when they rebound as the result of a rapid closure of the circuit breaker.

Many combinations of metal contacts have been tried in the endeavor to obtain contacts that have a low contact resistance, and which will not weld the contacts together under severe heating or arcing conditions incident to operation and interruption of thecircuit under severe load and short circuit'conditions. t

The present invention contemplates the use of 5 silver interspersed with finev particles of zirconium carbide.

The methods by which compositions of silver and zirconium carbide are produced may vary.

I may take, for instance, the powders of the car- 10 hides and mix them with the silver powder or a powdered silver base alloy consisting principally and essentially of silver. After an intimate mixture has been obtained, these; powders can be pressed either cold or at'elevated temperatures.

After the pressing, the powders may be sintered, either below the melting point of the low melting point metal, or above. After the sintering operation, the material may be repressed and resintered and then swaged, rolled or forged to any desirable shape, or it may be used inthe repressed condition. l

Another possibility where the higher percentages of zirconium carbide are used is to take the powderof zirconium carbide and press together, with or without the addition of a material or metal facilitating impregnation. After pressing and sintering, or after pressing, sintering, crushing, repressing and resintering, of the carbide, the silver may be introduced into the mixture by capillary action by contacting the sintered body with silver at temperatures above the melting point of the silver. Repressing and resintering, with or without further operations, may also be applied in this case. In certain instances, it has been found advisable to combine the above mentioned manufacturing procedures by substituting various steps of the one procedure with certain steps of the second procedure. Materials which 40 are usually helpful in obtaining complete impregnation are metals from the iron group or materials of the nature of silicon.

There are also possibilities of varying the impregnation process. It may, forinstance, be de- 45 sirable to spray the silver constituent on to the pressed carbine body and then heat same to absorb the sprayed layer of silver. Instead of spraying, other processes, such as plating, may be used. 50

By means of these methods, excellent metal compositions are obtained, the structures of which show good distribution of the ingredients, and the bodies of which may be easily prepared. Tests have shown that metallic bodies of the 56 above description are ideally suited for electrical contacting elements.-

Although from the nature'of the composition considerable variation can be made in the proportions of the ingredients depending, for instance, in case the capillary process'is used, on the percentage of voids in the sintered carbide before impregnation, I have found that the preferred proportions will generally fall within the range:

Per cent Zirconium carbide 1 to 50 Silver Balance One composition which has been found suitable for example contained:

' Per cent by weight Zirconium carbide 30 Silver '70 I have also found that carbides of zirconium may be used, which contain in combination a certain percentage of nitrogen.

Another advantage of the zirconium carbide is also its low specific gravity. The specific gravity of zirconium carbide is 6.90. For comparison, it

. might be stated that the specific gravity of tungsten carbide is 17.20, and that of tantalum carbide'is 14.49.-The melting point of zirconium carbide is 3,530 degrees C- Comparing this melting point with the melting point of tungsten carbide, which is used most frequently, or with molybdenum carbide, a great improvement can be noted, because the tungsten carbide melts. at

approximately 2,800 degrees C., while molybdenum carbide melts between 2600 and 2700 degrees C.

A further advantage is that zirconium carbide can be prepared at considerably lower cost than either molybdenum, tantalum or tungsten carbide. Furthermore, on account of the low specific gravityv a lower weight percentage of zirconium carbide is required in the mixture of silver and refractory carbide.

I have also found that electrical contacts prepared according to this disclosure work extremely well if the same compositions are used for both the negative and positive contact.

I have also found that these contacts will work very well with a large number of other com binations on the opposite side. By using this new and improved'composition on at least one side of a contact pair sticking and high contact resistance can be eliminated in most cases where it has usually occurred, with the present conin a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of. the invention herein described and all statements of the scope of the invention, which as a matter of language might be said to fall therebetween.

What is claimed is: 1. An electric contacting member formed of a composition comprising 1 to 50% zirconium carbide and the'balance essentially silver, the zirconium carbide being in a finely divided state intermingled with said silver, the composition a forming a compact solid mass.

2. An electric contact element formed of a metal composition composed of 1 to zirconium carbide and the balance substantially all silver.

FRANZ R. HENSEL. 

